There are difficulties in producing high tenacity multifilament yarns from long-term biodegradable copolymers of lactide/glycolide containing a majority of lactide. For example, in attempts to prepare multifilament yarns from such copolymers, it was found that excessive broken ends were generated in certain processes. In addition, the speed at which such a multifilament yarn is fed through the process had to be lowered to as low as 15 m/min in order to obtain acceptable process conditions and yarn properties.
U.S. Pat. No. 5,288,516 discloses a method to make high tenacity yarn with low incidence of filament breakage from a polyglycolic acid polymer at relatively high production speed. In this case, a lubricant was applied to the multifilament bundle, which then was drawn in 2 stages around a heated draw pin. However, this method cannot be applied to the Lactide rich copolymer because the melt-spun filaments made from such copolymers typically are too brittle to be drawn around a draw pin.
U.S. Pat. No. 5,232,648 and 5,425,984 disclose a low-shear extrusion process for making bioabsorbable yarns from a polymer containing 70-85% lactide. However, the resulting melt-spun filaments could be drawn only to a draw ratio of about 1.5xc3x97 to about 2.7xc3x97. In addition, maximum fiber tenacity achieved was 5.0-6.7 g/d, while the elongation was as low as about 14%. Such low elongation in the fiber can readily lead to excessive filament breakage and operational difficulties in the downstream processing, such as twisting and braiding the filaments together to make suture or other surgical articles.
U.S. Pat. No. 5,688,451 teaches the use of jet entanglement to imbed broken filaments in order to improve the downstream process. However, the broken filaments still are present in the product and typically are detected at the final inspection, causing rejection of product and reduced yield.
U.S. Pat. Nos. 5,585056 and 6,005,019 recommend plasticizers as process aids to improve yarn drawability and yarn properties. Although relatively high tenacity is achieved, the elongation at break of the suture made from a polymer, even with high percentage of flexible chains, e.g. 92.5:7.5 molar ratio poly(glycolide-co-lactide), still dropped to less than 20%.
It would be advantageous to provide a process for making long-term bioabsorbable, biocompatible multifilament yarn from Lactide rich copolymers for use in the fabrication of medical devices, e.g. sutures, surgical mesh, etc., which process produces improved yield of multifilament yarn at higher speeds, and which produces multifilament yarns of relatively high tenacity, elongation and work-to-rupture.
The present invention relates to a process of forming long-term bioabsorbable, biocompatible multifilament yarn from Lactide-rich copolymers, comprising the steps of extruding a copolymer comprising from about 80% to about 98% Lactide to form a multifilament spun yarn, applying a tension of at least about 5 grams to the spun multifilament yarn to form a pre-tensioned yarn, heating the pre-tensioned yarn at a temperature of from about 60xc2x0 C. to about 99xc2x0 C. for a period of not more than about 6 seconds to form a pre-tensioned, preheated yarn, annealing and drawing the pre-tensioned, preheated yarn for a first time by about 4xc3x97 to about 6xc3x97 at a temperature of from about 110xc2x0C. to about 150xc2x0 C. and for a time of from about 0.1 to about 2 seconds, annealing and drawing the yarn for a second time by about 1.05xc3x97 to about 1.3xc3x97 at a temperature of from about 60xc2x0 C. to about 150xc2x0 C. and for a time of from about 0.1 to about 2 seconds, preferably from about 0.3 to about 0.9 seconds, cooling the twice-drawn yarn to a lower temperature, and taking the multifilament yarn up. The process provides a long-term bioabsorbable, biocompatible multifilament yarn comprising from about 80% to about 98% Lactide having a tenacity of at least about 6 g/d, an elongation of at least about 26%, and work-to-rupture of at least about 20 g-cm/d. Surgical sutures also are provided which are manufactured from such multifilament yarn.